1. Field of the Invention
The present invention generally relates to a mobile-communications system, and a line concentrator, a wireless-base station, a mobile station and a communications method for use in the mobile-communications system.
2. Description of the Related Art
In current mobile-communications systems represented by the Third-Generation Mobile-Communications Systems, such method as, for example, WCDMA (Wideband Code Division Multiple Access) is being adopted, which method, from a point of view of efficiently using wireless-communications resources, changes the operational state of a mobile station depending on a period in which a packet is neither transmitted nor received. More specifically, the operational states consist of: a first state for using a dedicated channel to communicate (Cell-DCH); a second state such that a dedicated channel cannot be used but a common channel can be used (Cell-FACH); a third state for discontinuously receiving a control signal from a wireless-base station (Cell-PCH); and a fourth state such that no communications are conducted with the wireless-base station (Idle). These states are managed in a link layer (L2). In a wireless-access network in which the states of the mobile station are managed (UTRAN), which cell the mobile station in each of the first through third operational states belong to (which wireless-base station the mobile station is controlled by) is kept track of. When the cell to which the mobile station belongs changes (when the mobile station is handed over), a cell being managed at the UTRAN is also updated. It is noted that, for the mobile station in the third state, the UTRAN only keeps track of information of the cell last updated. Non-Patent Document 1, for example, discloses such a mobile-communications system.
On the other hand, in an existing mobile-communications system using an IP-compliant network, the states of the mobile station are managed in a network layer or an IP layer (L3) that is upper to the link layer. The states consist of a first state enabled to establish a wireless link so as to communicate (Active) and a second state such that the wireless link has been released (Dormant). The mobile station in the second state can receive a first signal (Router Advertisement) for broadcasting such information as which location-registration area is formed by multiple cells and a second signal (Paging Notification) for use in paging a mobile station. Configuring such a system makes it possible to always keep track of the location of the mobile station at the system side.
Non-Patent Document 1
Keiji Tachikawa et al., “W-CDMA mobile-communications method”, Maruzen, published Jun. 25, 2001